The objective of this protocol is to provide aliquots of hematopoietic stem cells from marrow and peripheral blood to investigators addressing multiple issues related to hematopoiesis. The source of these cells is donors of both allogeneic and autologous cells for use in the clinical transplant setting. Aliquots of stem cells have been utilized by investigators in the Department of Dermatology studying the generation of dendritic cells from hematopoietic stem cells. The Division of Neonatology in the Department of Pediatrics also studies dendritic cell development from the CD34+ hematopoietic stem cell. Investigators in the Division of Hematology have utilized hematopoietic stem cells in culture systems to generate human macrophage populations in order to define parameters affecting iron export from macrophages. Finally, Dr. Linda Kelley of the Division of Hematology has been utilizing stem cells from pheresis products to define the progenitors for megakaryocytes and early erythroid-committed lineages. All research reports resulting from the utilization of these cells credit the GCRC grant.